carb adjustment question

With the motor off, screw the small mixture screw in 'lightly' until it seats. Then back it out 2 1/2 complete turns. Start the motor, and adjust the bypass screw to obtain your idle at +- 850 RPM.

Your transmission, if anything, will get you BETTER mileage on the highway due to its shorter 4th gear.

Larry

Don't adjust the carb to make it leaner, follow the correct procedure and set the carb right!

Look at this site:

That's half the story, after this you have to find the highest RPM by adjusting the small mixture screw... It's all in the link I allready posted above.

Some timing adjuster thingies (stoboscope lamp?) have a precise rev-counter build in. Use that to monitor the RPM changes, very handy! If you don't have one, buy one!! Than you can also set your timing right.

Greetings, Gerrelt.

Is this on a bus or Bug? IMHO 26mpg in a Bus is pretty good, but sure, more is better. The tranny might indeed be messing up your mileage. The math tells us it should be better, but that presumes you have the power at cruising speed that optimizes at the RPM you are running.

Agree. Unfortunately its on my Bug.

--Dan E

Yeah, 26mpg is good for a carby Bug. Makes me wonder if he's braging or complaining.

Of, complaining. Maybe because I get 30mpg out of my Ghia with the same engine I am thinking I am coming up short on the Bug. But then, the Ghia has better aerodynamics which might account for the difference.

--Dan E

I wouldn't be surprised to find the Ghia more slippery in the wind. I'd like to find one I could afford.

Stafford's Right. The ghia is a more aerodynamic vehicle in all ways.............and is like ly the best reason for better MPG/KmPG. The Ghia has a very low drag coefficient , and compares to the porches of the day quite nicely.

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....s*it don't say that too loud, he might hear ya...then we are all doomed. ;-))

..>Gareth

So I guess he is right about 25mpg being pretty good mileage for a stock 1600 dp Bug?

--Dan E

With a carburated stock 1600 engine in good condition and properlly tuned you should be able to get 28-29 mpg at 70mph on the highway easilly. If the engine is worn and has many thousand miles on it, you might not be able to get better gas mileage. Otherwise, there are many factors that affect the gas mileage, such as the quallity of the engine rebuild and proper tunning, the fuel quality, the tire pressures, wheel allignment and weather conditions on the road.

Bill, '67 Bug.

The mixture screw only sets the idle circuit. The idle circuit is active up to 3000 rpm, but affects fuel consumption mostlly at low speeds, e.g in city traffic. The idle circuit has one sweet spot to which it must be set according to the procedure you can find easilly with a google search. You cannot just turn it a bit to richen or weaken the mixture.

By removing the spark plugs the next day (or when the engine cools down) after a highway trip, you can see if the main carb circuit is running rich. If the plugs are black from carbon deposits, you are running rich and you have to switch the main jet to something smaller. If you have a stock carb with the stock jets on a stock engine, it is unlikelly that you have to change the carb jetting.

Incorrect ignition timing, unadjasted valves, very low tire pressure and incorrect wheel allignment are things to check first.

Bill, '67 Bug.

On 11 Apr 2004 17:20:29 GMT, snipped-for-privacy@aol.comnojunk (Braukuche) ran around screaming and yelling:

depending on driving style, yes....a set of dual kads or icts will bump up the efficiency and get you a few more mpg... JT

That's a little dangerous advice, you are assuming the idle jet size is correct for the engine. The 2.5 turns out is just a starting point. That should get the thing running. The smaller the idle jet, the more you need to open the mixture screw.

So, set it at 2.5 turns out from fully seated position, start the car and set idle to something normal. I am assuming the timing and valves are adjusted already and engine is warmed up. Allow the auto choke to disengage and then start further adjusting the mixture. Turning the smell mixture screw in and out, in and out, you should be able to find a spot where you get the fastest idle, and more importantly the spot where the rpms stop to climb as you turn the screw out. Takes some time, it reacts a little slow and you should only do 1/2 turns at a time, then wait and see what effect it had. Find the spot where the idle doesn't climb anymore even if you were to turn the screw out one more 1/2 turn.. instead of doing so, turn it IN 1/2 turn and there you are. Now set idle speed to 900 with the larger idle bypass screw. I don't like to set the idle any lower, because on old and worn engines the oil pump won't hold pressure high enough when the engine is fully warmed up. Sitting at red lights idling away, red light flickering, is not a good thing for the engine.

Jan

One more factor: the precision of the odometer.

I gotta be wrong. My reputation is at stake here!

Dammit John, you are batting very well on this one. I thought about the speedo and its components too. However you stated it, not me. It is true that if you are calculating by the car's odometer , you should make damn sure it is accurate. If it only slips a tenth every couple of miles, that's a huge calculation issue................As well, you may just have wrong sized tires that makes the odo off a bit too........many things to consider, but keeping it simple is best , if at all possible. ( good call Stafford)

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